A rotary-type carburetor having a rotary throttle valve is often used in mixture passage which supplies a fuel-air mixture to an engine.
The rotary throttle valve in the rotary-type carburetor includes a block-type body having a bore with a circular cross section extending along an axis, and a valve element with a circular cross section to be contained in the bore. The body includes body passages extending from an upstream side to a downstream side so as to extend through the bore, while the valve element includes a valve passage extending through the valve element in a direction across the axis. The valve element is configured to rotate about the axis between a closed position where the valve passage is blocked from communicating with the body passages, and a fully-opened position where the valve passage and the body passages are aligned so as to define a maximum communication area.
The rotary-type carburetor also includes a carburetion nozzle unit disposed along the axis. The carburetion nozzle unit includes a cylindrical needle receiving part extending from a bore end part of the body through the valve element to the valve passage, and a needle extending from the valve element and being inserted into the needle receiving part. The needle receiving part includes a port for ejecting fuel into the valve passage. When the body passages and the valve passage are in communication with each other, fuel ejected from the port and vaporized is mixed with air flowing through the body passages and the valve passage and supplied to the engine (Please refer to the Patent Publications 1 and 2).
The valve element is also configured to move along the axis in a direction where the valve end part moves away from the bore end part when the valve element rotates from the closed position to the fully opened position so that the needle increases an opening area of the port. A small gap is provided between the valve element and the needle receiving part, enabling the rotation and the movement of the valve element.